To produce less expensive cans, for example, for beverages by deep drawing and stretch forming, experiments have been carried out for a long period of time in the use of untreated steel sheet for this purpose. Worthwhile results, however, have up to now not been obtained. Due to the locally high unit pressure during the stretch-forming operation, even when high pressure lubricants are used, after a short period of time, galling will occur between the workpiece and the tool caused by local welding of the steel onto the necessary hard metal tools. Therefore, at the present time beverage cans are being manufactured of tin-plated steel sheet (tin plate). The tin-plating acts as a separating layer and avoids such galling.
It is also known in other areas of this type of technology that phosphatized sheet metal, that is, sheet metal, which is provided with a thin phosphate coating, tends at the most to undergo only a minor degree of galling during a deep-drawing operation. However, the phosphatizing must be effected by a special operation and subsequently the phosphatized sheet metal must still be provided with an oil film which prevents rusting of the sheet metal and furthermore acts as a lubricant during the deep drawing. Due to these additional method steps, the phosphatized sheet metal cannot be manufactured at any appreciably less cost than tin-plated sheet metal.
In order to carry out the phosphatizing and the application of the lubricant in one operation, an acid reaction lubricant is known under the term Bonderlube 460 and 461 (Registered Trademark). This acid reaction lubricant Bonderlube 460 and 461 is sold by Metallgesellschaft AG Frankfurt (Main). It contains both a phosphatizing medium and a lubricant. In such treatment the annealed steel strip is dipped for a substantial period of time into the liquid, which liquid contains the phosphatizing medium and the lubricant. The bath temperature is normally at 65.degree.-70.degree. C., and the dipping time is approximately 10 minutes. After the treatment, the treated strip must hang for approximately 5 minutes above the bath container so that most of the excess lubricant can run off. Prior to the further deformation, the strip is permitted to assume room temperature in an inclined position. Through the treatment in the mentioned liquid, both a phosphate layer and also a lubricant layer is produced in the strip. The phosphate layer has the characteristic of better holding of the lubricant and the lubricant serves to protect against rust. During the cold forming the phosphate layer acts as a separating layer and the lubricant acts to lubricate the operation.
However, in this method, there exists the disadvantage that the strip must be dipped for a relatively long period of time into the liquid. Thus, it is not possible, or it is possible only with a considerable expense, to proceed immediately after the annealing with the phosphatizing, because either the annealing would have to be carried out extremely slowly or, following the continuous furnace, a correspondingly long bath would have to be available so that the strip, from the time of its entering into the bath until it exits therefrom, remains at a travelling speed which is the same as that used for the continuous annealing. However, such a method would be just as uneconomical as the separate continuous annealing at a normal strip speed and the phosphatizing at a low strip speed in a separate method step.
Thus, the basic purpose of the invention is to improve a method for the manufacture of a cold-rolled steel strip in thin and super-thin strip thicknesses for producing stretch-formed cans or other deep-drawn parts of the above-mentioned type in a less expensive manner than was previously known.